Most high frequency radio modules, for example, a high frequency radio transceiver module, use several circuit boards on which electronic components are mounted to reduce module costs or optimize module size. These module costs can be further reduced by mounting only high frequency components on those boards that require more expensive circuit components and materials, for example, by mounting microwave monolithic integrated circuit (MMIC) chips on a ceramic board, and forming a radio frequency (RF) transceiver board. The less expensive low frequency circuit components, for example, power and DC circuit components, can be mounted on less expensive boards, for example, conventional printed wiring boards. Some of these boards can be formed from a copper clad epoxy substrate or glass reinforced resin substrate board, such as FR4 board. The module size can be optimized by either stacking or overlapping the circuit boards. Unfortunately, board-to-board connectors with good performance become more difficult to fabricate and are more expensive as the frequencies being transferred between the different boards increase. At moderate and millimeter wave frequencies, the problem is exacerbated.
Traditionally, moderate frequency board-to-board connections have been accomplished by using miniature, coaxial board-to-board connectors. These coaxial connectors typically are cylindrical, and include a central conductor that could be solid or stranded wire inside a cylindrical, metallic housing, tube or shielded conductor, and separated by a dielectric material in the form of spacers or cylindrical and solid continuous extrusion. An insulating jacket may be included. An outer conductor in this type of connector is typically at ground potential and acts as a return path for current through the central conductor. It also can prevent energy radiation. This outer conductor or shield can also prevent external radiation from affecting the current in the inner or central conductor. An example of such a connector is shown in FIG. 1 and shows a central conductor and external conductor separated by a dielectric. This connector often has to be machined, and the dielectric and central conductor inserted, sometimes complicating the manufacture. As a result, miniature coaxial connectors used for board-to-board connections are relatively expensive and do not have adequate ground connections for high frequency operation and transfer.
Commonly assigned U.S. Pat. No. 6,625,881, issued Sep. 30, 2003, the disclosure which is hereby incorporated by reference in its entirety, discloses a connector system and method for connecting cooperating printed circuit boards and transferring high frequency radio frequency signals between the printed circuit boards. A housing member has a clip receiving slot and circuit board engaging surface that is positioned against a first printed circuit board. At least one electrically conductive clip member has opposing ends and is received within the clip receiving slot. One end is secured to a circuit on the first printed circuit board and the other end is biased in the connection with the circuit of a second printed circuit board. High frequency radio frequency signals are transferred from one printed circuit board to the other printed circuit board via the clip member.
Other techniques used to transfer high frequency signals from one printed wiring board to another board would be advantageous, however, especially between various types of boards, for example, between a printed wiring board (PWB) having lower frequency and/or less expensive components, for example, DC signal and power components, and a ceramic board that mounts high frequency and/or more expensive components, for example, microwave monolithic integrated circuit (MMIC) chips.